Hemoproteins are connected intrinsically with many key cellular processes such as reversible oxygen binding, oxygen storage, peroxide destruction, and electron transfer reactions. They contain two types of components: metal-containing porphyrins and apoproteins. The combination of these two components, when properly configured, provides functionally-active porphyroproteins (e.g., hemoglobin).
A variety of medical and commercial processes require large amounts of specific porphyroproteins for uses such as blood replacement, food modification, biochemical reactions, and the like. Historically, these needs have been met by the isolation and purification of naturally-occurring porphyroproteins, but these sources increasingly are coming back under attack because they can harbor infectious particles, including prions, and because they can cause antigenic reactions in people due to species' differences in the proteins.
Recently, efforts have been directed toward avoiding some of these problems by producing species-specific apoproteins (e.g., human-type globin) in fermentation/incubation and modified-animal systems using genetically-modified cells. Such procedures can provide species-specific apoproteins, and fermentation/incubation procedures can also provide apoproteins (proteins without their associated co-factors) free of animal-derived infectious particles.
One approach to manufacturing hemoglobin involves adding hemin (a porphyrin) to globin (an apoprotein) isolated from a natural source (such as blood), which combine, under appropriate conditions, with each other to form hemoglobin in vitro. A variation of this approach involves adding hemin to a culture/fermentation medium containing bacterial or yeast cells which have been genetically engineered to produce globin in the cell. In this latter in vivo method, the host cell takes up the hemin which has been added to the culture/fermentation medium and combines the hemin in vivo with the globin. The resulting hemoglobin can be removed from the host cell using conventional cell lysis techniques. However, in these methods, the porphyrin portion of the haloproteins must still be produced by isolation from natural sources such as animal blood.
There are at least four major problems associated with such isolation procedures from natural sources:
1. There is a serious concern about infectious particles, including prions and prion fragments, being present. This is a major ethical and liability concern. PA1 2. There is a relatively high cost of extracting porphyrins from natural sources. PA1 3. There are serious religious prohibitions in many groups whose rules proscribe products either from certain kinds of animals, from animals of any kind, or from animal blood. PA1 4. There are major governmental regulatory problems regarding natural animal products.
The concern about infectious particles can be met partially by subjecting the porphyrins to very harsh acid and high temperature conditions that are known to degrade various microorganisms and viruses. However, recent research on prions ("infectious protein molecules") has shown that it is not possible to know for sure how much degradation is necessary to lose such "infectiousness". And, even if infectivity is not a problem, there still remain problems of high cost, sources of origin and governmental regulations.